1. Field of the Invention
This invention relates to physiological stress testing devices for medical diagnostics, and particularily to devices of the type employing a motor powered moving surface commonly known as a treadmill.
2. Description of a Related Art
Exercise treadmills have been used extensively as diagnostic and therapeutic devices. They are particularly well suited to the evaluation and study of heart and lung diseases in that they provide a continuous and programmable level of activity. Although electrocardiograms taken from resting patients are useful for some types of physiological defects, there are many abnormalities which will go undetected unless the patient is subjected to a certain threshold level of energy output. The ability of the treadmill to provide an accurate and predictable level of continuous exercise--representing a constant workload--graded at various time intervals, has led to its widespread use as aid in medical diagnosis and patient evaluation.
Traditional treadmills utilize an induction motor which is speed controlled by a triac or other AC switching device which varies the conduction angle to provide sufficient power to maintain the desired velocity. At maximum speeds, i.e., when the conduction angle approaches 180.degree. of each half cycle, the motor operates efficiently, and the ratio of power supplied to the belt to the input power is maximized. When the same motor is operated at a slow belt speed however, the conduction angle is reduced to a small fraction of the full cycle. Because of the combined effect of the reduced back emf and the short duration of the applied power, the motor current flows in high amplitude, short duration pulses. The I.sup.2 R losses are thus multiplied and the overall efficiency of the system is materially reduced. For effective operation with reasonably sized motors, a 220 volt source is required.
It is thus a primary objective of the present invention to provide a electronic system for operating a treadmill over a range of velocities utilizing a standard 110 volt power source.
The problem of operating at low velocities is compounded by the intermittent nature of the load. As the patients foot propels him forward to maintain his relative velocity with respect to the belt, the load increases sharply and then drops abruptly to zero--the effect being to introduce an additional variable in the form of a reoccurring impulse load. It is thus a further object of the present invention to provide a buffer between the motor and belt which will smooth out the load reflected to the motor.
A third and interrelated aspect of the present invention is an electronic braking system which abruptly stops the motor in the event of an emergency.
Other objects and advantages of the present invention will be obvious from the detailed description of a preferred embodiment given herein below.